Vertical takeoff and landing aircraft (VTOL's) are generally well known. See, for example: Nahodyl U.S. Pat. No. 4,085,911, issued Apr. 25, 1978; Bachman U.S. Pat. No. 3,863,869, issued Feb. 4, 1975; Riccius U.S. Pat. No. 3,801,048, issued Apr. 2, 1974; and Jaeger U.S. Pat. No. 3,640,489, issued Feb. 8, 1972. Simiarly, vertical and short takeoff and landing aircraft (V/STOL's) are also well known. See, Lincks et al. U.S. Pat. No. 3,703,266, issued Nov. 21, 1972 and Haberkorn U.S. Pat. No. 3,645,476, issued Feb. 29, 1972. These apparatus achieve vertical lift by generating a downward thrust of sufficient magnitude to overcome gravitational forces. However, the necessarily large mass and energy consumption requirements of these jet propulsion systems make them impractical and prohibitively expensive for recreational use.
Another well-known method of producing vertical lift involves the use of an airfoil configured to effect more rapid motion of the fluid medium (air) over the upper surface than over the lower surface of a wing during forward motion thereof. As the air velocity along the upper wing surface increases, the static pressure decreases. To the extent a sufficient pressure differential is maintained between the upper and lower surfaces of the wing, vertical lift may be sustained. However, high velocity ram air, corresponding to high forward aircraft velocity, is needed to create an adequate pressure differential. Consequently, conventional airfoil systems are unsatisfactory in circumstances where a runway is unavailable or vertical takeoff is otherwise desirable.
Airfoil systems have been suggested for use in conjunction with vertical thrust systems. See, for example, Clover U.S. Pat. No. 3,243,146, issued Mar. 29, 1966. Moreover, attempts have been made to adapt the Coanda effect to aircraft propulsion. The Coanda effect is defined as the tendency of a fluid stream to "attach" itself to an adjacent surface. See, for example, Whittley U.S. Pat. No. 3,429,527, issued Feb. 25, 1969 and Viets U.S. Pat. No. 4,392,621, issued July 12, 1983. Specifically, a generally horizontal exhaust stream is directed over the upper surface of a wing configured to curve downwardly in the aft direction. The stream tends to attach itself to the curved surface, producing a downward and rearward exhaust stream. Thus, even though the exhaust stream is ejected, for example from a jet engine, in a substantially horizontal plane, the Coanda effect due to the convex wing induces a vertical thrust component.
The disadvantage of the Coanda effect, particularly when used as the sole source of vertical lift, resides in the inability to pump a sufficient volume of air to overcome the gravitational forces associated with jet propulsion systems.
The need to reduce total system mass, and thereby maintain thrust requirements and fuel consumption within reasonable limits, has resulted in the emergence of the ultralight aircraft industry. By keeping gross system weight low, for example under 254 pounds, relatively inexpensive recreational aircraft, using various vertical lift systems, are now available. However, these vehicles are unable to achieve vertical takeoff. See, for example, Cronk et al. U.S. Pat. No. 4,372,506, issued Feb. 8, 1983; Schmittle U.S. Pat. No. 4,595,368, issued June 24, 1986; Dempsey U.S. Pat. No. 4,548,371, issued Oct. 22, 1985; and Schmittle U.S. Pat. No. 4,568,043, issued Feb. 4, 1986.